Use of otolith microstructure to study life history of juvenile chinook salmon in the Strait of Georgia in 1995 and 1996

The pattern of otolith daily increments was used to identify hatchery-reare d, wild ocean-type and wild stream-type chinook and study their life histor y in the Strait of Georgia. In 1995 and 1996, almost all of hatchery-reared and wild stream-type chinook entered the Strait of Georgia in May and June , while wild ocean-type chinook entered from April to August. Upon ocean en try stream-type fish were the largest and wild ocean-type the smallest. Hat chery-reared and wild ocean-type chinook leaving fresh water later in the y ear were larger than those leaving earlier. The mean length of wild stream- type chinook was not related to the time of ocean entry. All the life histo ry types maintained their size differences throughout the summer and fall d espite some differences in rates of size increase. Hatchery-reared and wild stream-type chinook grew faster in 1995 than in 1996. Wild ocean-type grew at about the same rate. During early summer, the percentage of wild ocean- type chinook was low in contrast to the percentage of hatchery-reared and w ild stream-type chinook in 1995 and 1996, respectively. In September of bot h years, the percentage of wild ocean-type chinook increased and the percen tage of hatchery-reared and wild stream-type chinook dropped. By November i n both years, the percentage of hatchery-reared chinook increased, especial ly in 1996 when the percentage exceeded 80%. After the first ocean winter, the percentage of hatchery-reared fish remained high. (C) 2000 Elsevier Sci ence B.V. All rights reserved.